Light- How much light is around us and what does it mean for photography

While deleting some images on my computer, I came across this old image/graph that mentioned typical light intensity for different situations. This can be helpful to know limitation of cameras in low light. If you want to take good photos in low light with your iPad or iPhone and if you are not able to do so, it is not your fault.
In graph below, we are not supposed to remember various numbers but this one does show how dramatically light varies from situation to situation. In outdoor under mid day Sun compared to a bright indoor room, light intensity is 500 times more! When you compare this bright mid day under Sun to an indoor dim room, the light intensity is 6000 times more!

Clear Full Moon light is around .03 Lux. Typical Starlight is around .001 Lux.

So up to 500 Lux, a handheld camera can take good sharp photos IMHO (my guess). However to take good photos in situations with lesser light, we need either a tripod or faster and/or bigger sensor cameras and a stationary

Practical considerations for Light and Exposure in day to day use:

* iPhone 6 has widest aperture of 2.2. Assuming ISO of 400 (beyond 400, images will be grainy) and very stable hands, you can take shutter speed of 1/75 seconds.
With this, the lowest light you will need to take sharp good photos with your iPhone 6 is around 226 Lux. This means in brightly lit homes or in offices to outdoor photos, an iPhone or any latest smartphone camera can be useful.
If you like to use ISO at 100 only, you will need 907 Lux of light intensity.

* On the other extreme, high end full frame SLR with a fast lens of f/1.2 can take good photos even at ISO 3200. Assuming same shutter speed of 1/75 seconds, it can take good photos in light as low as 9 Lux!

If you have a Lux meter, you can use this equation (Lux= Square of F number * 1/shutter speed * (250 /ISO)) for determining the variables like Shutter Speed needed, or ISO needed for a given aperture. The discussion in this post is  mostly to get a feel about what is going on when you press the shutter release button in any camera. In reality, when you press the button, the sensors and computers inside you camera, takes the reading of the light in the frame and uses some equation like above to set up aperture opening, shutter speed and/or ISO depending on the mode. If you shoot in Manual, you provide the numbers and camera stops thinking. If you are in A or Av mode, you tell camera what value to use for aperture. If you have set up ISO too, camera will determine shutter speed based on some equation like the one above.

So ignoring bokeh or image sharpness with faster lens and bigger sensors on DSLR, an iPhone or any smartphone or a fixed lens camera can take good photos in light that is 200 Lux or more. This means well lit indoor or bright outside. With bigger bodies and more investment, you can go down as low as 10 Lux hand-holding your camera which would be Family living room lights, relatively dim indoor, office building hallways or very dark overcast day.

Now with a tripod and if you subject is stationary, you can go and shoot in almost any situation. If you want to shoot stars though, you need only a high end DSLR as if you go beyond exposure of 10-20 seconds, you will capture movement of stars.

Hope this helps.

Sources:
If you want to get into technicality of exposure, here is a nice summary on DPReview chat. Not sure if it is accurate but it mentions that

N^2/t = L*ISO / (10/0.67)

....for ISO = 100, N = 2.8, t = 1/100, and a calibration constant K = 12.5, the required luminance would be about

L = 2.8^2*100*12.5/100 = 98 cd per sq. meter

to produce a middle grey tone in your final image. Illumination is trickier, and a typical calibration constant is 250 for incident light measured in lux. So for this same example we would need

L = 2.8^2*100*250/100 = 1960 lux.

I know LUX is very confusing measure compared to meter or centimeter for length, pound or kg for weight or second/minute for time. Lux measures intensity of light. Instead of getting into technicals of it, I would rather remember relative values so you can understand how it affects photography.

If you want the definition of Lux, here it is from Wikipedia.

"The lux (symbol: lx) is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area.^[1] It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, oflight that hits or passes through a surface. It is analogous to the radiometric unit watts per square metre, but with the power at each wavelength weighted according to the luminosity function, a standardized model of human visual brightness perception. In English, "lux" is used in both singular and plural.^[2]"

Here are some examples of the illuminance provided under various conditions:(Source: Wikipedia

Examples
Illuminance	Surfaces illuminated by:
0.0001 lux	Moonless, overcast night sky (starlight)[3]
0.002 lux	Moonless clear night sky with airglow[3]
0.27–1.0 lux	Full moon on a clear night[3][4]
3.4 lux	Dark limit of civil twilight under a clear sky[5]
50 lux	Family living room lights (Australia, 1998)[6]
80 lux	Office building hallway/toilet lighting[7][8]
100 lux	Very dark overcast day[3]
320–500 lux	Office lighting[6][9][10][11]
400 lux	Sunrise or sunset on a clear day.
1000 lux	Overcast day;[3] typical TV studio lighting
10000–25000 lux	Full daylight (not direct sun)[3]
32000–100000 lux	Direct sunlight

Canon T5i or T4i? EOS 700D or Nikon D7000? Which camera is good in low light?

Once you buy your first DSLR, you mostly get disappointed by indoor or low light photos. Probably you expected your sort of expensive purchase to do wonders but most of them with their ordinary kit lens can do little bit batter than compact cameras but when light is really insufficient, they don't have magic to take great photos. This then takes you in your next pursuit for a camera that can taken nice photos indoor or in low light. You can run variety of searches for low light performance of Canon 700D vs Nikon D3200 or T4i vs Sony NEX cameras. You will read conflicting opinions and will likely to get lost. In my opinion, there is not much difference between any Canon or Nikon, or Sony or Panasonic which have similar sensor sizes and are released in the market not much apart in time. I would advise you not to get lost in the war of Nikon Vs Canon.
Here is a 2 minute primer for you.

Which camera works better in low light?

Remember these quick rules for low light shooting. It is the sensor size and sensor technology that determines the performance of camera in low light.
Normally,
* Bigger the sensor, the better the camera works in low light.
* Newer the sensor, usually the camera works better in low light. An APS-C sized sensor of Canon XS or XTi does not work as good as same sized sensor in Canon 650D or T5i. Canon XS photos with ISO800 may not be usable but T5i photos with ISO 3200 may be totally usable!
* For the same sensor size, the lower the mega pixels of camera, the better it is for low light shooting. Sounds stupid, right? However if you put too many mega pixels on the same sized sensor, the sensitivity of the sensor suffers and so does its low light performance. This is because each pixel becoming smaller and hence losing some quality with respect to light sensitivity. (Read this article about what is optimum MP that I should use on my camera.)


It is not the Camera body; it is the lens that does wonders in low light
Last but not the least, most kit lenses are very very slow. Most kit lens are F3.5 which are not that great when it comes to take in light. If you want to have better low light performance, you can buy fast 1.4 or 1.8 lens and your ability to shoot in low light will go up exponentially. What an F1.8 lens can achieve in low light compared to a F3.5 kit lens, spending even $1000 more on camera body can not do! If you are going to stick to kit lens only, your best bets are Canon EOS-M that comes with 22mm F2 lens or Pentax K-01 which comes with 40mm F2.8 lenses. I have both of them (and had some other regular DSLRs too) and I can say that they take much better photos in low light than T4i or D7000. Both of these camera bodies have top tier sensor size, technology and image quality. Now 700D (t5i) does have a good lens but it will cost 2-3 times more than the two cameras I have listed above. With the money saved, I would buy a fast 35 or 50mm F1.4 lens and most people would wow at your low light photos.
Your might like to read about my favorite DSLR value buy these days (2013)


Use Tripod
Now if you are taking low light photos, see what you are shooting. If you are shooting people or pets, even a tripod will not help you. Most of us move quick enough and will produce a blurry image. Now if you are taking photos of still objects, a tripod can come very handy. There is no simple set up for this but I would keep ISO to 100 (unless you are taking photos of plants where leaves can move or you are shooting the Moon of any even slow moving object), and f at 8-11 in Av mode. Or f at 2 to 5 if you need faster shutter speed and narrower depth of field. Will write more about this later some time but till then, please remember that it is not the camera that takes better photos; it is you who can take better photos with most cameras in most situations by becoming more pro-active.

Enjoy digital photography.
In last one decade more animals in the zoo are shot with digital cameras then the animals shot together over last 1000 years LOL. Once you buy a camera, it doesn't cost much to keep shooting.